Microfluidic Tissue Engineering of Small Airway Injuries This project brings together microfluidic, computational, and animal model expertise to evaluate the relative roles of solid- and fluid-mechanical stresses causing, or exacerbating, or predisposing injury of small airway epithelia. This proposal focuses on small airways because they are implicated as the first level of damage in acute respiratory distress syndrome (ARDS) (1, 2). These airways are subject to closure and reopening during the ventilatory cycle, and can be injured from the associated mechanics called atelectrauma. Since these airways are coated with a liquid lining, all closure and reopening involves the formation, propagation, and rupture of liquid plugs. Our previous work (3, 4) showed that fluid/surface tension forces from propagating and, especially, rupturing liquid plugs are a significant cause of lethal injury to airway epithelial cells cultured on microfluidic, lung-on-chip platforms. Animal models have also shown that a higher surface tension due to reduction in concentrations of pulmonary surfactants as the major cause of small airway atelectrauma (5), while plug ruptures with acoustical signatures are particularly associated with airway injury (6). Here, we propose to determine the mechanism of atelectrauma while separating out the contributions of elastic vs fluid/surface tension forces in experiment and computations. We hypothesize that fluid/surface tension mechanical forces in atelectrauma are a major contributor to ARDS. We will also test the role of atelectrauma in the exacerbation of additional insults such as, bacterial infection and acid aspiration, which are direct risk factors for the development of ARDS. Although low tidal volumes have been shown to reduce mortality in patients with ARDS, the benefits of the open lung ventilation concept remain controversial. One of the major reasons for the variable results of open lung ventilation stems from the lack of understanding of the best way to prevent atelectasis. Understanding the mechanism of small airway atelectrauma is essential for developing successful therapeutic interventions in ARDS. While our main goal is to clarify fundamental mechanisms underlying ARDS pathology, our findings have significant clinical implications. We have the potential to clarify whether personalized, appropriate levels of PEEP or recruitment maneuvers may prevent atelectrauma and thereby result in mitigation of lung injury in ARDS. The aims are designed to answer key questions such as: What is the relative contribution of stretch versus fluid mechanical stress in causing lung injury? How will combined insults of fluid mechanical stress together with acid aspiration or bacterial insult exacerbate lung injury?